A major complaint about Google's Chrome web browser has been that so far, it is still not available on anything other than Windows. Google promised to deliver Chrome to Mac OS X and Linux as well, but as it turns out, this is a little harder than they anticipated, Ben Goodger, Google's Chrome interface lead, has explained in an email. It has also been revealed what toolkit the Linux version of Chrome will use: Gtk+.

I think the point is that Google wasn't satisfied with the Lowest Common Denominator that the available toolkits offer.

Fact is, outside of Firefox & Adobe, there is no major piece of software that uses a cross-platform toolkit across Mac & Windows. And both these companies UIs have often been criticized for not behaving / appearing correct on the Mac (and I have heard similar complaints about the Windows versions as well).

And it doesn't have to be as complicated as you make it sound. You will have one team working on the rendering engine, which will be cross-platform, and one team each working on the wrapper for each platform. Considering that there are small companies like Omni & Shiira that are able to develop their own browser for a Mac, I'm sure Google has enough guys to work on the Mac platform, Linux platform, and Windows platform.